Coal gasification is a well known process for the conversion of coal solids into gaseous fuel. In the prior art, a fluidized bed reaction of carbon with water and some oxygen forms a mixture of methane, carbon monoxide and hydrogen. This mixture, called synthesis gas, is an easily transported fuel.
The process is known to be highly endothermic, requiring continuous massive inputs of heat to sustain a reaction. In a full-scale plant based on coal-oxygen-steam gasification, usually at least 30 wt. % of the coal is consumed in supplying needed process input heat and steam, and hence only about 70 wt. % of the coal is effectively converted to useful commercial fuel. When one takes into account additional coal used for power generation at a typical plant, the net conversion of coal to commercial fuel can be as low as 50 to 60 wt. % overall. In addition considerable amounts of oxygen are consumed, typically about 0.5 ton of oxygen per ton of coal throughput.
Biomass solids are becoming increasingly available, and like coal are difficult to transport. The similar endothermic conversion of carbonaceous biomass solids in a fluidized bed with steam forming synthesis gas is currently being debated, but tends not to be attractive due to the massive energy inputs required, just to sustain the reaction.
It would be very desirable to be able to gasify these carbonaceous materials without consuming large amounts of oxygen and the carbonaceous materials themselves during heat generation for the process.
With this in mind, attempts have been made to utilize solar energy as the source of heat necessary to promote the gasification reaction. One such attempt is disclosed in U.S. Pat. No. 3,993,458 issued to Antal on Nov. 23, 1976. In this patent, solar energy is introduced directly into the gasification reactor through quartz windows.
There are many disadvantages inherent in introducing solar energy into a reactor in the fashion disclosed by Antal. Solar energy input is lessened due to blackening of the quartz input window by tar, coke and ash formation. Additionally, since the coal is not transparent, solar heating is limited to the small zone directly adjacent the solar window. This may result in overheating in areas adjacent the solar window and subsequent reactor damage.
It is therefore desirable to have a solar powered gasification system which introduces the solar energy into the gasification system in an efficient and effective manner.